Why won't this loop populate my array ?

Hello

I'm writing a loop to populate array A with the averages of the columns of array B.

 w =[100.0000   90.0000   81.0000   72.9000   65.6100;
            0  110.0000   99.0000   89.1000   80.1900;
            0         0  121.0000  108.9000   98.0100;
            0         0         0  133.1000  119.7900;
            0         0         0         0  146.4100]

B =

Columns 1 through 11

100.0000  100.0000  100.0000  100.0000  100.0000  100.0000  100.0000  100.0000  100.0000  100.0000  100.0000  
 90.0000   90.0000   90.0000   90.0000  110.0000   90.0000   90.0000   90.0000  110.0000  110.0000  110.0000   
 81.0000   81.0000   81.0000   99.0000   99.0000   81.0000   99.0000   99.0000   99.0000   99.0000  121.0000   
 72.9000   72.9000   89.1000   89.1000   89.1000   89.1000   89.1000  108.9000   89.1000  108.9000  108.9000  
 65.6100   80.1900   80.1900   80.1900   80.1900   98.0100   98.0100   98.0100   98.0100   98.0100   98.0100  

Columns 12 through 16

100.0000  100.0000  100.0000  100.0000  100.000   
110.0000  110.0000  110.0000  110.0000  110.000
121.0000  121.0000  121.0000  121.0000  121.000
108.9000  133.1000  133.1000  108.9000  133.100
119.7900  119.7900  119.7900  119.7900  146.410

I'm trying to create an array 'A' such that each row vector is a set of averages for the given stock price. However my output is always an array of zeros, the loop is not pushing any values to A. Please help. Thank you very much for your help in advance.

n=4 
A= zeros(n+1)
for J=1:n+1;
    for i=1:2^(n);%loops through every column of B
        if w(J,n+1)==B(n+1,i);% if the last value of W equals the last value of B 
          A(J,1:end)=sum(B(:,i))/(n+1);% take the average of that column B and place it in matrix A 

         end 
     end
end
A

[David Fletcher]

If you want the mean of the columns in B you can just use

A=mean(B)

However, the likely reason you are failing to get anything other than zeros is that the condition if w(J,n+1)==B(n+1,i) is never equating to true, so A will always equal the pre-allocation of zeros(n+1)

Answer 1

[KSSV]

You need not to run a loop to get averages...read about mean. It can calculate averages along row and columns by sppecifying dimesnion. If you are stringent in using loops, check below code. Let W be your matrix of size mxn where you want to get averages of columns.

[m,n]=size(W);
iwant=zeros(1,n);
for i=1:n
  iwant(I)=sum(W(:,i))/m ;
end

[michaelsmith]

yeah thanks, I want to average each column in 'B' but arrange the averages in an array so that each row will be a set of averages relating to the same final stock price B(n+1,i).

Thats where I am having difficulty.

Answer 2

[Image Analyst]

It looks like you have w and just want the mean of non-zero values in w, so why not simply do

A = sum(w, 1) ./ sum(w ~= 0, 1);